The present invention relates to a CT couch apparatus having a lift employed by the radiation computed tomography apparatus and serving to move up and down the table top of the couch on which the patient lies so as to place the patient inside the opening of the scan gantry and pull him back from the opening.
In order to obtain tomographic images of the patient with the radiation CT apparatus or X-ray CT apparatus, for example, it is necessary that the patient is located exactly at the predetermined position inside the opening of the scan gantry.
FIG. 1 shows the conventional CT couch, located behind a scan gantry 10 when viewed in a direction shown by an arrow 4, and a mounting frame 16, supported on a base 14 by means of a pair of parallel arms 20 and 22. The arms 20 and 22 are not moved relative to each other but rotatably connected to the base 14 and mounting frame 16. A patient couch 18 can be shifted longitudinally in relation to its mounting frame 16.
The arms 20 and 22 are sloped to the greatest extent thereof and a patient 2 is laid down on the couch 18 in this condition. The arms 20 and 22 are then rotated and erected by means of a hydraulic pump (not shown) to lift the mounting frame 16. When the patient 2 is lifted to the predetermined position behind an opening 12 of the scan gantry 10, the lifting of the mounting frame 16 is stopped. Linear crossing light beams 24 are projected toward the patient 2 at this predetermined position, and the position of the couch 18 is adjusted to accord the ear hole of the patient 2 with the crossing point of the crossing light beams 24. The couch 18 is then shifted relative to the mounting frame 16 and that part of the patient 2 which is to be scanned with X-rays is located at a tomographic image position 26 inside the opening 12.
When the patient 2 at the predetermined position is lower than an area 28 inside the scan gantry 10 where tomographic images of the patient 2 are obtained, it is necessary that the arms 20 and 22 are further rotated to make the position of the mounting frame 16 higher. However, the mounting frame 16 is moved forward in the direction 4 by the rotation of the arms 20 and 22. For the purpose aligning the ear hole of the patient 2 with the crossing point of the crossing light beam 24, therefore, it is necessary that the couch 18 be moved backward in relation to the mounting frame 16 when viewed in the direction 4. Several processes are necessary to position the patient, thereby making the operation complicated. In addition, an AC motor is usually used to move the couch 18, but it is likely to move the couch 18 beyond a predetermined position, thereby making it difficult to exactly locate the couch 18. A DC motor may be used to avoid this, but a DC motor is expensive.
Since the arms 20 and 22 are parallel to each other, they have a limited sloping angle, thereby making it difficult to locate the couch 18 at a low position.